A traditional injection molding system melts a material, such as a plastic, primarily by shear heat that is dynamically generated by rotation of a screw. The traditional injection molding system features a barrel with an opening at a hopper where plastic pellets enter the system and a nozzle where the plastic exits the barrel during injection. Between the hopper opening and the nozzle, the screw places pressure on the plastic resin to generate shear heat, bringing the plastic melt to the injection zone during a recovery extrusion stage of the molding cycle. This shear heat generation system relies on the formation of a cold slug in the nozzle to contain the plastic between each shot. The cold slug seals the nozzle after the injection cycle and prevents additional plastic from flowing out through the nozzle during the recovery extrusion stage that is between molding shots, trapping plastic in the barrel so that pressure can be applied to generate shear heat. However, the cold slug requires very high pressure to be dislodged to allow molten resin to flow out through the nozzle during the next injection cycle. The pressure applied to dislodge the cold slug is largely absorbed by the volume of plastic between the screw tip and the nozzle. Once the cold slug is dislodged, high pressure pushes the resin melt into a mold cavity through a mold gate (e.g., an entrance to the mold cavity) and runners or channels for delivering the melt into the mold cavity. It is common for a traditional injection molding system to have an injection pressure between 20,000 and 30,000 psi in order to obtain a pressure of 500-1500 psi in the mold cavity. Due to the high pressure, the traditional injection molding system typically includes a barrel having a heavy or thick wall section, which reduces the heat conduction to the plastic from the band heaters that surround the barrel. The cold slug causes one of the greatest inefficiencies for the traditional injection molding system.
Documents that may be related to the present disclosure in that they include various injection molding systems include U.S. Pat. No. 7,906,048, U.S. Pat. No. 7,172,333, U.S. Pat. No. 2,734,226, U.S. Pat. No. 4,154,536, U.S. Pat. No. 6,059,556, and U.S. Pat. No. 7,291,297. These proposals, however, may be improved.
There still remains a need to resolve the issues of the present injection molding systems to develop an automated and more efficient system that may provide additional flexibility for various applications.